摘要: 為探討橋梁斷面的非線性自激氣動(dòng)力,基于平衡位置的Taylor級(jí)數(shù)展開式,建立了簡諧運(yùn)動(dòng)下橋梁斷面非線性自激氣動(dòng)力模型,獲得了其復(fù)數(shù)和實(shí)數(shù)表達(dá)式,并說明了表達(dá)式中非線性氣動(dòng)參數(shù)的識(shí)別方法.該模型反映了簡諧運(yùn)動(dòng)下橋梁斷面非線性自激氣動(dòng)力的諧波疊加特性,可應(yīng)用于橋梁的非線性氣動(dòng)穩(wěn)定性分析.最后,應(yīng)用該模型對(duì)某橋梁斷面在簡諧運(yùn)動(dòng)下的非線性自激氣動(dòng)力風(fēng)洞試驗(yàn)時(shí)程數(shù)據(jù)進(jìn)行了擬合.擬合結(jié)果表明,兩者的誤差在3%以內(nèi),驗(yàn)證了該模型的正確性.
關(guān)鍵詞: 橋梁斷面;非線性自激氣動(dòng)力;經(jīng)驗(yàn)?zāi)P停伙L(fēng)洞試驗(yàn)
中圖分類號(hào): V211.24文獻(xiàn)標(biāo)志碼: AEmpirical Mathematical Model for Nonlinear MotionInduced
當(dāng)橋梁斷面在氣流中運(yùn)動(dòng)時(shí),會(huì)對(duì)流場產(chǎn)生干擾,引起表面壓力的變化,從而產(chǎn)生隨時(shí)間變化的空氣動(dòng)力,稱為自激氣動(dòng)力.
1971年,Scanlan提出了用顫振導(dǎo)數(shù)表示的橋梁斷面自激氣動(dòng)力模型[1],將氣動(dòng)力表示為斷面運(yùn)動(dòng)狀態(tài)的線性函數(shù),并在此基礎(chǔ)上提出了橋梁顫振臨界風(fēng)速的計(jì)算方法.事實(shí)上,橋梁斷面屬于鈍體,其自激氣動(dòng)力應(yīng)是非線性的,并已在風(fēng)洞試驗(yàn)中獲得證實(shí)[26].尤其對(duì)于形式上為典型鈍體的橋梁斷面,其自激氣動(dòng)力的非線性效應(yīng)更加突出.因此,橋梁斷面自激氣動(dòng)力應(yīng)考慮非線性效應(yīng).
徐旭和曹志遠(yuǎn)基于瞬態(tài)風(fēng)攻角推導(dǎo)了橋梁等柔長結(jié)構(gòu)沿跨向分布的非線性氣動(dòng)力表達(dá)式[78].Diana基于墨西拿大橋斷面的風(fēng)洞試驗(yàn)結(jié)果,提出了以瞬態(tài)攻角(位移)及其一階導(dǎo)數(shù)(速度)為變量的非線性氣動(dòng)力表達(dá)式[56,910].Chen和Ma基于橋梁的軟顫振現(xiàn)象,提出了用范德波爾方程來描述非線性氣動(dòng)力和軟顫振現(xiàn)象的思路[11].Wu和Kareem從橋梁斷面的非線性響應(yīng)出發(fā),提出了一個(gè)基于Volterra泛函級(jí)數(shù)的非線性氣動(dòng)力模型[1213].Zhang、Chen等通過對(duì)大跨度橋梁非線性顫振的分析,分別提出了考慮紊流風(fēng)影響的非線性氣動(dòng)力模型[1415].
在上述非線性氣動(dòng)力的典型模型中,徐旭提出的模型過于復(fù)雜,也沒有給出非線性氣動(dòng)參數(shù)的識(shí)別方法,因此在實(shí)踐中無法應(yīng)用.Diana提出的模型能夠較好地描述試驗(yàn)獲得的非線性氣動(dòng)力,但模型的適用性和適用范圍還需要進(jìn)一步研究;Chen和Ma提出的范德波爾模型無法描述非線性氣動(dòng)系數(shù)隨振幅變化的非定常性,并暗含氣動(dòng)力只含有三次諧波分量,因此該模型具有很大的局限性;Wu和Kareem提出的Volterra泛函級(jí)數(shù)模型能夠描述氣動(dòng)力的非線性和非定常性,但目前還處于初步研究階段,并需要可靠的風(fēng)洞試驗(yàn)數(shù)據(jù)作為支撐;Zhang、Chen等提西南交通大學(xué)學(xué)報(bào)第48卷第2期王騎等:橋梁斷面非線性自激氣動(dòng)力經(jīng)驗(yàn)?zāi)P统龅哪P?,?shí)際上是考慮主梁的幾何非線性效應(yīng)和風(fēng)攻角的非線性后提出的修正氣動(dòng)力模型,其實(shí)質(zhì)為參數(shù)非線性變化的線性氣動(dòng)力模型.
綜上所述,目前對(duì)于橋梁斷面非線性自激氣動(dòng)力模型的研究還處于起步階段.因此,合理、適用、簡便的自激氣動(dòng)力模型亟待研究.
本文以簡諧運(yùn)動(dòng)下橋梁斷面的自激氣動(dòng)力為
研究對(duì)象,基于平衡位置的Taylor級(jí)數(shù)展開式,建立了由不同諧波分量疊加的非線性氣動(dòng)力數(shù)學(xué)模型,推導(dǎo)了非線性自激氣動(dòng)力的復(fù)數(shù)和實(shí)數(shù)表達(dá)式,并簡要介紹了表達(dá)式中非線性氣動(dòng)參數(shù)的識(shí)別方法;基于某橋梁斷面非線性自激氣動(dòng)力的風(fēng)洞試驗(yàn)測試數(shù)據(jù),用該模型進(jìn)行了擬合,兩者的誤差小于3%,從而驗(yàn)證了該模型的正確性.1簡諧運(yùn)動(dòng)下的Taylor展開式處于均勻流場中的橋梁斷面,自激氣動(dòng)力為其運(yùn)動(dòng)狀態(tài)的函數(shù),并可表示為動(dòng)態(tài)的氣動(dòng)力形式(某一時(shí)刻的氣動(dòng)力).
考慮到橋梁斷面的自激氣動(dòng)力主要與其豎向和扭轉(zhuǎn)運(yùn)動(dòng)狀態(tài)相關(guān),其氣動(dòng)升力L和力矩M可分別表示為:
6結(jié)語以在氣流中保持簡諧運(yùn)動(dòng)的橋梁斷面為研究對(duì)象,基于平衡位置的Taylor級(jí)數(shù)展開式,建立了橋梁斷面的非線性氣動(dòng)力模型,推導(dǎo)了不同運(yùn)動(dòng)條件下非線性自激氣動(dòng)力的表達(dá)式,從理論上闡述了簡諧運(yùn)動(dòng)下橋梁斷面的非線性自激氣動(dòng)力由不同倍頻或非倍頻諧波分量共同組成的特性,并基于等效關(guān)系,給出了非線性氣動(dòng)參數(shù)的表達(dá)式.
風(fēng)洞試驗(yàn)結(jié)果表明,簡諧運(yùn)動(dòng)下橋梁斷面的自激氣動(dòng)力是由不同諧波分量組成的,且以二次和三次諧波分量為主.對(duì)試驗(yàn)信號(hào)的擬合結(jié)果表明,所提出的氣動(dòng)力模型能夠準(zhǔn)確地描述橋梁斷面的非線性自激氣動(dòng)力.
由于試驗(yàn)條件限制,只選取了一種試驗(yàn)斷面,并在單自由度條件下對(duì)模型進(jìn)行了驗(yàn)證.為了深入研究橋梁斷面自激氣動(dòng)力的非線性效應(yīng),今后還需要針對(duì)更多斷面形狀、在不同運(yùn)動(dòng)形式下(包括耦合運(yùn)動(dòng)和任意運(yùn)動(dòng)形式)進(jìn)行理論研究和風(fēng)洞試驗(yàn),以擴(kuò)展和補(bǔ)充理論模型.
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(中、英文編輯:付國彬)